FYI, I've been writing a series of articles on throw effects for Billiards Digest. They can be found here (http://www.engr.colostate.edu/~dga/pool/bd_articles/index.html). The first six articles (August '06 through January '07) are already posted, and future articles in the series will be posted as they become available. I'll post some of the Q&amp;A's I've had to date, and feel free to post additional comments and questions.

Thanks,
Dr. Dave

PS: FYI, I've answered questions dealing with past articles in another thread (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=167746&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;fpart=1); but it was getting a bit long, so I thought I'd start new threads for each new major topic.

dr_dave

12-01-2006, 10:18 AM

<blockquote><font class="small">Quote BD reader:</font><hr>Question re your November column (http://www.engr.colostate.edu/~dga/pool/bd_articles/2006/nov06.pdf): WHY is it that the amount of SIT drops off beyond 35% english? Swerve?<hr /></blockquote>
First of all, swerve is not the reason. I have not accounted for swerve in the current analysis. In all of the throw articles, I am assuming that the shooter is already compensating for squirt and swerve (or that the effects are small). I will cover swerve effects in future articles.

To answer your main question: For small amounts of spin, the friction (throw) force between the balls is large enough to limit the amount of slipping between the ball surfaces. As the amount of spin is increased, the speed of relative sliding motion between the balls increases. Friction is smaller at higher relative surface speeds, so the amount of throw is less.

Sorry I couldn't come up with a simpler answer. This is tough to describe because there is a lot of physics going on.

Regards,
Dr. Dave

dr_dave

12-01-2006, 10:34 AM

<blockquote><font class="small">Quote BD reader:</font><hr>How’s this analogy? Once your tires are spinning on the ice, faster spinning only makes them slipperier. You have to slow the spin down to get more grab, contrary to your “common sense”.<hr /></blockquote>
Nice job! That works for me.

Regards,
Dr. Dave

<blockquote><font class="small">Quote dr_dave:</font><hr> <blockquote><font class="small">Quote BD reader:</font><hr>Question re your November column (http://www.engr.colostate.edu/~dga/pool/bd_articles/2006/nov06.pdf): WHY is it that the amount of SIT drops off beyond 35% english? Swerve?<hr /></blockquote>
First of all, swerve is not the reason. I have not accounted for swerve in the current analysis. In all of the throw articles, I am assuming that the shooter is already compensating for squirt and swerve (or that the effects are small). I will cover swerve effects in future articles.

To answer your main question: For small amounts of spin, the friction (throw) force between the balls is large enough to limit the amount of slipping between the ball surfaces. As the amount of spin is increased, the speed of relative sliding motion between the balls increases. Friction is smaller at higher relative surface speeds, so the amount of throw is less.

Sorry I couldn't come up with a simpler answer. This is tough to describe because there is a lot of physics going on.

Regards,
Dr. Dave <hr /></blockquote>

dr_dave

12-01-2006, 10:39 AM

<blockquote><font class="small">Quote BD reader:</font><hr>In the Dec installment (http://www.engr.colostate.edu/~dga/pool/bd_articles/2006/dec06.pdf) did you take squirt into account?<hr /></blockquote>No. I will cover this in future articles. In the current series, so far, I have assumed that the shooter is compensating for squirt and swerve in their aim (or the effects are small for the example shots).

<blockquote><font class="small">Quote BD reader:</font><hr>Did the cue ball squirt and that compensated for the extra sit?<hr /></blockquote>No.